Bone marrow-derived fibroblasts in skin wound healing. Nearly 25% of all diabetic patients, with foot ulcers, will inevitably progress to major limb amputation. Diabetic wound healing deficiencies are associated with impaired tissue level neovascularization, impaired keratinocyte function, reduced tensile strength, and higher infection rates. While these generalized poor wound healing defects of patients with diabetes mellitus are well established, the specific tissue level mechanisms responsible for these wound-healing deficiencies remain poorly understood. A complex cellular cascade mediates normal cutaneous wound healing, where all skin cells cooperate to repair and rebuild the dermis and epidermis. But in patients with chronic wounds, these signals for cell recruitment, proliferation, and differentiation in the wound bed are disrupted. Overall, we aim to develop new strategies for treating chronic leg wounds by primarily identifying specific molecules, that when expressed by cells within the wound itself, will promote healing of chronic wounds as well as fully restore skin architecture and function. Because fibroblasts are the critical cell type for early and late wound healing, we hypothesize that, during normal wound healing, fibroblast precursor cells are recruited from both, the resident resting pool in the skin and the bone marrow-derived stem cell populations, which then subsequently migrate into the wound bed and differentiateinto mature fibroblasts. To distinguish between these two cellular populations we have developed in vivo bone marrow transplantation models, using normal and diabetic mice, and novel in vitro three-dimensional reconstructions of human dermis, vascularized dermis, and skin, in which fibroblasts can interact with other key cell types involved in wound healing. In these in vivo wound-healing models and in vitro reconstructionswe will determine the extent to which bone marrow-derived fibroblasts influence wound- healing processes including contraction of collagen, stimulation of vessel formation, re-epithelialization and keratinocyte growth and differentiation. With the use of viral vector delivery of agonists and inhibitors, we will test the hypothesis that growth factors, specifically PDGF-B (platelet-derived growth factor) are critical for the activation of bone marrow-derived fibroblasts to invade into collagen, proliferate, migrate to the wound, survive, and differentiate into long-term cellular components of the healed skin wound.